1. Field of the Invention
The present invention generally relates to a movement detection circuit for television signals and particularly relates to a circuit for extracting movement information of an object included in a composite color television signal in which a chrominance signal modulated by a subcarrier is superimposed on a luminance signal.
In the specification of this application, the "motion information of an object" is not for the detection of direction or distance of movement but for the detection of a temporal variation in pixel level (amplitude).
2. Description of the Prior Art
An inter-frame video coder for processing television signals by using a frame memory (or field memory), a frame-recursive noise reducer, a separation circuit for separating a luminance signal and a chrominance signal from each other, a scanning line interpolating circuit, and so on, are known as means for processing motion picture signals. In those means, how to extract motion information of an object has been a serious problem. In the case of a monochromatic television signal, motion information of an object can be extracted on the basis of the magnitude of an inter-frame difference signal calculated by using a frame memory. On the other hand, in the case of a composite color television signal in which a chrominance signal modulated with a subcarrier frequency f.sub.ac is superimposed on a luminance signal like an NTSC signal, the phase of the subcarrier of the frequency f.sub.ac modulating the chrominance signal changes in every frame so that a modulated chrominance signal may leak into the inter-frame difference signal in addition to the motion information to thereby make it impossible to obtain correct movement information.
In a conventional motion detection circuit, as described in Japanese patent unexamined publication No. 130685/83, motion information has been obtained on the basis of the magnitude of an operational signal such as an inter-frame or inter-field sum or difference of modulated chrominance signal. The above-mentioned operational signal has the subcarrier frequency f.sub.ac as its central frequency, so that its amplitude ripples with a frequency of 1/2f.sub.ac so as to cause a dot structure of produce stationary areas in a moving area. There has been caused, therefore, such a problem that the picture quality in the moving area rather deteriorates in the case where such an operational signal is utilized as movement information.